The process of dental bleaching is an increasingly popular practice in dentistry to combat the problem of staining or discoloration of teeth.
The enamel layer of teeth is composed of hydroxyapatite. It is believed that the porous nature of the enamel is attributed to the crystalline structure of hydroxyapatite, which allows staining agents and discoloring substances to permeate the enamel, thereby discoloring teeth. Substances that come in contact daily with teeth and that can stain or reduce the “whiteness” of teeth include foods, tobacco products, tea, coffee, betel nut, plants and food products. These substances permeate the enamel of the teeth and with continued contact impart noticeable discoloration to the teeth.
In addition, teeth may become stained from excessive intake of fluoride (endemic fluorosis). In young persons, the administration of tetracycline during tooth formation may cause staining. Generalized intrinsic staining can result from systemic conditions and diseases such as cystic fibrosis, congenital hematoporphia and dentinogenesis imperfecta.
Since white or unstained teeth are considered to improve a person's appearance, it is generally desired by patients to try to increase the whiteness of the teeth. Methods of improving the whiteness of teeth include bleaching methods which can be used to ameliorate the staining of teeth. However, known effective bleaching procedures for teeth also result in the undesired effect of tending to produce hypersensitivity or supersensitivity of the teeth. It has been reported that 74% of incidents of dental bleaching result in post-bleaching pain (hypersensitivity) to the patient. Bleaching compositions generally use peroxide or peroxide yielding compounds which have tended to involve the activation of peroxide by light sources such as photo flood light, ultraviolet light, or by heat methods such as convection heat or by the application of heat directly to teeth. These methods require the use of high concentrations of peroxide, such as in the form of Superoxol® or a 35% peroxide composition, which not only cause hypersensitivity but also have the potential to damage oral and facial tissues.
Passive bleaching involves the use of bleaching agents supplied directly in dentrifice compositions for brushing the teeth, or gels, foams, creams or pastes which are applied in prefabricated trays and/or in custom trays fabricated with reservoirs to hold bleaching preparations in extended intimate contact with the teeth for longer periods of time. Passive bleaching agents have been used with photo flood lights and with lasers. It is now understood that the teeth can be made whiter by passive bleaching methods using peroxide releasing compounds such as carbamide peroxide, also known as urea peroxide, usually in the amount of 10% to 20% by weight of the composition. The higher concentrations of the peroxide yielding compounds are used to effect faster and more effective bleaching (power bleaching). Other peroxide releasing compounds that have been known in the prior art include sodium perborate, zinc peroxide, calcium peroxide and magnesium peroxide, and other compounds which can release peroxide effectively with bubbling oxidizing force.
In general, higher concentrations of peroxide yielding compounds improve the efficacious bleaching capabilities of the composition. However, the higher peroxide concentrations exacerbate the sequelae of hypersensitivity or supersensitivity. The pain resulting from hypersensitivity or supersensitivity is considered to be a warning that the tooth and pulpal tissues have experienced a severe insult. Faster and more aggressive bleaching techniques, such as with the use of higher concentrations of peroxide yielding compounds, results in more severe and higher incidence of post-bleaching hypersensitivity to thermal, chemical and tactile stimuli.
Dental bleaching compositions are described in a number of references, including U.S. Pat. Nos. 5,098,303; 5,234,342; 5,376,006; and 5,409,63 1, all to Fischer, which are hereby incorporated by reference. The Fisher patents describe tooth bleaching dental gel composition comprising carbamide peroxide, water, glycerin, carboxypolymethylene (Carbopol) and sodium hydroxide. Dental bleaching compositions are also described in U.S. Pat. No. 5,631,000, to Pellico et al., which is hereby incorporated by reference.
The use of potassium nitrate as a compound for desensitizing teeth is disclosed in U.S. Pat. No. 3,863,006, which is hereby incorporated by reference. Potassium nitrate has also been disclosed as useful for treatment of canker sores in U.S. Pat. No. 4,191,750, hereby incorporated by reference; useful for preserving dental pulp, in U.S. Pat. No. 4,343,608, hereby incorporated by reference; useful for treating gingival and periodontal tissues, in U.S. Pat. No. 4,400,373, hereby incorporated by reference; and useful for treating post-restoration dental pain, in U.S. Pat. No. 5,153,006, hereby incorporated by reference.
Other patents, including for example U.S. Pat. Nos. 5,256,402 and 5,648,399, have described the use of potassium nitrate in dentrifice compositions as a treatment for hypersensitivity. However, the use of potassium nitrate incorporated into dental tray bleaching compositions has not been previously described as being capable of preventing tooth hypersensitivity.
Another patent, U.S. Pat. No. 5,522,726 has described the use of a composition having a high concentration of potassium, such as potassium nitrate, for anesthetizing teeth requiring preparation, caries removal or manual manipulation thereof.